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;;; diff-mode.el --- a mode for viewing/editing context diffs
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;; Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004,
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;;   2005, 2006, 2007, 2008 Free Software Foundation, Inc.
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;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
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;; Keywords: convenience patch diff
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;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation; either version 3, or (at your option)
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;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
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;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.
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;;; Commentary:

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;; Provides support for font-lock, outline, navigation
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;; commands, editing and various conversions as well as jumping
;; to the corresponding source file.

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;; Inspired by Pavel Machek's patch-mode.el (<pavel@@atrey.karlin.mff.cuni.cz>)
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;; Some efforts were spent to have it somewhat compatible with XEmacs'
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;; diff-mode as well as with compilation-minor-mode

;; Bugs:

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;; - Reverse doesn't work with normal diffs.
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;; Todo:

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;; - Improve `diff-add-change-log-entries-other-window',
;;   it is very simplistic now.
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;;  
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;; - Add a `delete-after-apply' so C-c C-a automatically deletes hunks.
;;   Also allow C-c C-a to delete already-applied hunks.
;;
;; - Try `diff <file> <hunk>' to try and fuzzily discover the source location
;;   of a hunk.  Show then the changes between <file> and <hunk> and make it
;;   possible to apply them to <file>, <hunk-src>, or <hunk-dst>.
;;   Or maybe just make it into a ".rej to diff3-markers converter".
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;;   Maybe just use `wiggle' (by Neil Brown) to do it for us.
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;;
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;; - in diff-apply-hunk, strip context in replace-match to better
;;   preserve markers and spacing.
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;; - Handle `diff -b' output in context->unified.
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;;; Code:
(eval-when-compile (require 'cl))

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(defvar add-log-buffer-file-name-function)

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(defgroup diff-mode ()
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  "Major mode for viewing/editing diffs."
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  :version "21.1"
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  :group 'tools
  :group 'diff)

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(defcustom diff-default-read-only nil
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  "If non-nil, `diff-mode' buffers default to being read-only."
  :type 'boolean
  :group 'diff-mode)

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(defcustom diff-jump-to-old-file nil
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  "Non-nil means `diff-goto-source' jumps to the old file.
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Else, it jumps to the new file."
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  :type 'boolean
  :group 'diff-mode)
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(defcustom diff-update-on-the-fly t
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  "*Non-nil means hunk headers are kept up-to-date on-the-fly.
When editing a diff file, the line numbers in the hunk headers
need to be kept consistent with the actual diff.  This can
either be done on the fly (but this sometimes interacts poorly with the
undo mechanism) or whenever the file is written (can be slow
when editing big diffs)."
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  :type 'boolean
  :group 'diff-mode)
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(defcustom diff-advance-after-apply-hunk t
  "*Non-nil means `diff-apply-hunk' will move to the next hunk after applying."
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  :type 'boolean
  :group 'diff-mode)
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(defcustom diff-auto-refine t
  "Automatically highlight changes in detail as the user visits hunks."
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  :type 'boolean
  :group 'diff-mode)
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(defcustom diff-mode-hook nil
  "Run after setting up the `diff-mode' major mode."
  :type 'hook
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  :options '(diff-delete-empty-files diff-make-unified)
  :group 'diff-mode)
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(defvar diff-outline-regexp
  "\\([*+][*+][*+] [^0-9]\\|@@ ...\\|\\*\\*\\* [0-9].\\|--- [0-9]..\\)")

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;;;;
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;;;; keymap, menu, ...
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;;;;
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(easy-mmode-defmap diff-mode-shared-map
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  '(;; From Pavel Machek's patch-mode.
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    ("n" . diff-hunk-next)
    ("N" . diff-file-next)
    ("p" . diff-hunk-prev)
    ("P" . diff-file-prev)
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    ("\t" . diff-hunk-next)
    ([backtab] . diff-hunk-prev)
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    ("k" . diff-hunk-kill)
    ("K" . diff-file-kill)
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    ;; From compilation-minor-mode.
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    ("}" . diff-file-next)
    ("{" . diff-file-prev)
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    ("\C-m" . diff-goto-source)
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    ([mouse-2] . diff-goto-source)
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    ;; From XEmacs' diff-mode.
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    ;; Standard M-w is useful, so don't change M-W.
    ;;("W" . widen)
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    ;;("." . diff-goto-source)		;display-buffer
    ;;("f" . diff-goto-source)		;find-file
    ("o" . diff-goto-source)		;other-window
    ;;("w" . diff-goto-source)		;other-frame
    ;;("N" . diff-narrow)
    ;;("h" . diff-show-header)
    ;;("j" . diff-show-difference)	;jump to Nth diff
    ;;("q" . diff-quit)
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    ;; Not useful if you have to metafy them.
    ;;(" " . scroll-up)
    ;;("\177" . scroll-down)
    ;; Standard M-a is useful, so don't change M-A.
    ;;("A" . diff-ediff-patch)
    ;; Standard M-r is useful, so don't change M-r or M-R.
    ;;("r" . diff-restrict-view)
    ;;("R" . diff-reverse-direction)
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    ("q" . quit-window))
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  "Basic keymap for `diff-mode', bound to various prefix keys.")
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(easy-mmode-defmap diff-mode-map
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  `(("\e" . ,diff-mode-shared-map)
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    ;; From compilation-minor-mode.
    ("\C-c\C-c" . diff-goto-source)
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    ;; By analogy with the global C-x 4 a binding.
    ("\C-x4A" . diff-add-change-log-entries-other-window)
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    ;; Misc operations.
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    ("\C-c\C-a" . diff-apply-hunk)
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    ("\C-c\C-e" . diff-ediff-patch)
    ("\C-c\C-n" . diff-restrict-view)
    ("\C-c\C-s" . diff-split-hunk)
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    ("\C-c\C-t" . diff-test-hunk)
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    ("\C-c\C-r" . diff-reverse-direction)
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    ("\C-c\C-u" . diff-context->unified)
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    ;; `d' because it duplicates the context :-(  --Stef
    ("\C-c\C-d" . diff-unified->context)
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    ("\C-c\C-w" . diff-ignore-whitespace-hunk)
    ("\C-c\C-b" . diff-refine-hunk)  ;No reason for `b' :-(
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    ("\C-c\C-f" . next-error-follow-minor-mode))
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  "Keymap for `diff-mode'.  See also `diff-mode-shared-map'.")

(easy-menu-define diff-mode-menu diff-mode-map
  "Menu for `diff-mode'."
  '("Diff"
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    ["Jump to Source"		diff-goto-source
     :help "Jump to the corresponding source line"]
    ["Apply hunk"		diff-apply-hunk
     :help "Apply the current hunk to the source file and go to the next"]
    ["Test applying hunk"	diff-test-hunk
     :help "See whether it's possible to apply the current hunk"]
    ["Apply diff with Ediff"	diff-ediff-patch
     :help "Call `ediff-patch-file' on the current buffer"]
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    ["Create Change Log entries" diff-add-change-log-entries-other-window
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     :help "Create ChangeLog entries for the changes in the diff buffer"]
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    "-----"
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    ["Reverse direction"	diff-reverse-direction
     :help "Reverse the direction of the diffs"]
    ["Context -> Unified"	diff-context->unified
     :help "Convert context diffs to unified diffs"]
    ["Unified -> Context"	diff-unified->context
     :help "Convert unified diffs to context diffs"]
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    ;;["Fixup Headers"		diff-fixup-modifs	(not buffer-read-only)]
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    "-----"
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    ["Split hunk"		diff-split-hunk
     :active (diff-splittable-p)
     :help "Split the current (unified diff) hunk at point into two hunks"]
    ["Ignore whitespace changes" diff-ignore-whitespace-hunk
     :help "Re-diff the current hunk, ignoring whitespace differences"]
    ["Highlight fine changes"	diff-refine-hunk
     :help "Highlight changes of hunk at point at a finer granularity"]
    ["Kill current hunk"	diff-hunk-kill
     :help "Kill current hunk"]
    ["Kill current file's hunks" diff-file-kill
     :help "Kill all current file's hunks"]
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    "-----"
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    ["Previous Hunk"		diff-hunk-prev
     :help "Go to the previous count'th hunk"]
    ["Next Hunk"		diff-hunk-next
     :help "Go to the next count'th hunk"]
    ["Previous File"		diff-file-prev
     :help "Go to the previous count'th file"]
    ["Next File"		diff-file-next
     :help "Go to the next count'th file"]
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    ))

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(defcustom diff-minor-mode-prefix "\C-c="
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  "Prefix key for `diff-minor-mode' commands."
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  :type '(choice (string "\e") (string "C-c=") string)
  :group 'diff-mode)
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(easy-mmode-defmap diff-minor-mode-map
  `((,diff-minor-mode-prefix . ,diff-mode-shared-map))
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  "Keymap for `diff-minor-mode'.  See also `diff-mode-shared-map'.")

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;;;;
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;;;; font-lock support
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;;;;
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(defface diff-header
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  '((((class color) (min-colors 88) (background light))
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     :background "grey80")
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    (((class color) (min-colors 88) (background dark))
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     :background "grey45")
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    (((class color) (background light))
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     :foreground "blue1" :weight bold)
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    (((class color) (background dark))
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     :foreground "green" :weight bold)
    (t :weight bold))
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  "`diff-mode' face inherited by hunk and index header faces."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-header-face 'face-alias 'diff-header)
(defvar diff-header-face 'diff-header)
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(defface diff-file-header
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  '((((class color) (min-colors 88) (background light))
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     :background "grey70" :weight bold)
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    (((class color) (min-colors 88) (background dark))
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     :background "grey60" :weight bold)
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    (((class color) (background light))
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     :foreground "green" :weight bold)
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    (((class color) (background dark))
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     :foreground "cyan" :weight bold)
    (t :weight bold))			; :height 1.3
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  "`diff-mode' face used to highlight file header lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-file-header-face 'face-alias 'diff-file-header)
(defvar diff-file-header-face 'diff-file-header)
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(defface diff-index
  '((t :inherit diff-file-header))
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  "`diff-mode' face used to highlight index header lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-index-face 'face-alias 'diff-index)
(defvar diff-index-face 'diff-index)
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(defface diff-hunk-header
  '((t :inherit diff-header))
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  "`diff-mode' face used to highlight hunk header lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-hunk-header-face 'face-alias 'diff-hunk-header)
(defvar diff-hunk-header-face 'diff-hunk-header)
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(defface diff-removed
  '((t :inherit diff-changed))
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  "`diff-mode' face used to highlight removed lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-removed-face 'face-alias 'diff-removed)
(defvar diff-removed-face 'diff-removed)
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(defface diff-added
  '((t :inherit diff-changed))
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  "`diff-mode' face used to highlight added lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-added-face 'face-alias 'diff-added)
(defvar diff-added-face 'diff-added)
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(defface diff-changed
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  '((((type tty pc) (class color) (background light))
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     :foreground "magenta" :weight bold :slant italic)
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    (((type tty pc) (class color) (background dark))
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     :foreground "yellow" :weight bold :slant italic))
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  "`diff-mode' face used to highlight changed lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-changed-face 'face-alias 'diff-changed)
(defvar diff-changed-face 'diff-changed)
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(defface diff-indicator-removed
  '((t :inherit diff-removed))
  "`diff-mode' face used to highlight indicator of removed lines (-, <)."
  :group 'diff-mode
  :version "22.1")
(defvar diff-indicator-removed-face 'diff-indicator-removed)

(defface diff-indicator-added
  '((t :inherit diff-added))
  "`diff-mode' face used to highlight indicator of added lines (+, >)."
  :group 'diff-mode
  :version "22.1")
(defvar diff-indicator-added-face 'diff-indicator-added)

(defface diff-indicator-changed
  '((t :inherit diff-changed))
  "`diff-mode' face used to highlight indicator of changed lines."
  :group 'diff-mode
  :version "22.1")
(defvar diff-indicator-changed-face 'diff-indicator-changed)

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(defface diff-function
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  '((t :inherit diff-header))
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  "`diff-mode' face used to highlight function names produced by \"diff -p\"."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-function-face 'face-alias 'diff-function)
(defvar diff-function-face 'diff-function)
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(defface diff-context
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  '((((class color grayscale) (min-colors 88)) :inherit shadow))
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  "`diff-mode' face used to highlight context and other side-information."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-context-face 'face-alias 'diff-context)
(defvar diff-context-face 'diff-context)
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(defface diff-nonexistent
  '((t :inherit diff-file-header))
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  "`diff-mode' face used to highlight nonexistent files in recursive diffs."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-nonexistent-face 'face-alias 'diff-nonexistent)
(defvar diff-nonexistent-face 'diff-nonexistent)
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(defconst diff-yank-handler '(diff-yank-function))
(defun diff-yank-function (text)
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  ;; FIXME: the yank-handler is now called separately on each piece of text
  ;; with a yank-handler property, so the next-single-property-change call
  ;; below will always return nil :-(   --stef
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  (let ((mixed (next-single-property-change 0 'yank-handler text))
	(start (point)))
    ;; First insert the text.
    (insert text)
    ;; If the text does not include any diff markers and if we're not
    ;; yanking back into a diff-mode buffer, get rid of the prefixes.
    (unless (or mixed (derived-mode-p 'diff-mode))
      (undo-boundary)		; Just in case the user wanted the prefixes.
      (let ((re (save-excursion
		  (if (re-search-backward "^[><!][ \t]" start t)
		      (if (eq (char-after) ?!)
			  "^[!+- ][ \t]" "^[<>][ \t]")
		    "^[ <>!+-]"))))
	(save-excursion
	  (while (re-search-backward re start t)
	    (replace-match "" t t)))))))
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(defconst diff-hunk-header-re-unified
  "^@@ -\\([0-9]+\\)\\(?:,\\([0-9]+\\)\\)? \\+\\([0-9]+\\)\\(?:,\\([0-9]+\\)\\) @@")
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(defvar diff-font-lock-keywords
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  `((,(concat "\\(" diff-hunk-header-re-unified "\\)\\(.*\\)$")
     (1 diff-hunk-header-face) (6 diff-function-face))
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    ("^\\(\\*\\{15\\}\\)\\(.*\\)$"                        ;context
     (1 diff-hunk-header-face) (2 diff-function-face))
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    ("^\\*\\*\\* .+ \\*\\*\\*\\*". diff-hunk-header-face) ;context
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    ("^--- .+ ----$"             . diff-hunk-header-face) ;context
    ("^[0-9,]+[acd][0-9,]+$"     . diff-hunk-header-face) ;normal
    ("^---$"                     . diff-hunk-header-face) ;normal
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    ;; For file headers, accept files with spaces, but be careful to rule
    ;; out false-positives when matching hunk headers.
    ("^\\(---\\|\\+\\+\\+\\|\\*\\*\\*\\) \\([^\t\n]+?\\)\\(?:\t.*\\| \\(\\*\\*\\*\\*\\|----\\)\\)?\n"
     (0 diff-header-face)
     (2 (if (not (match-end 3)) diff-file-header-face) prepend))
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    ("^\\([-<]\\)\\(.*\n\\)"
     (1 diff-indicator-removed-face) (2 diff-removed-face))
    ("^\\([+>]\\)\\(.*\n\\)"
     (1 diff-indicator-added-face) (2 diff-added-face))
    ("^\\(!\\)\\(.*\n\\)"
     (1 diff-indicator-changed-face) (2 diff-changed-face))
    ("^Index: \\(.+\\).*\n"
     (0 diff-header-face) (1 diff-index-face prepend))
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    ("^Only in .*\n" . diff-nonexistent-face)
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    ("^\\(#\\)\\(.*\\)"
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     (1 font-lock-comment-delimiter-face)
     (2 font-lock-comment-face))
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    ("^[^-=+*!<>#].*\n" (0 diff-context-face))))
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(defconst diff-font-lock-defaults
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  '(diff-font-lock-keywords t nil nil nil (font-lock-multiline . nil)))
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(defvar diff-imenu-generic-expression
  ;; Prefer second name as first is most likely to be a backup or
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  ;; version-control name.  The [\t\n] at the end of the unidiff pattern
  ;; catches Debian source diff files (which lack the trailing date).
  '((nil "\\+\\+\\+\\ \\([^\t\n]+\\)[\t\n]" 1) ; unidiffs
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    (nil "^--- \\([^\t\n]+\\)\t.*\n\\*" 1))) ; context diffs

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;;;;
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;;;; Movement
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;;;;
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(defvar diff-valid-unified-empty-line t
  "If non-nil, empty lines are valid in unified diffs.
Some versions of diff replace all-blank context lines in unified format with
empty lines.  This makes the format less robust, but is tolerated.
See http://lists.gnu.org/archive/html/emacs-devel/2007-11/msg01990.html")

(defconst diff-hunk-header-re
  (concat "^\\(?:" diff-hunk-header-re-unified ".*\\|\\*\\{15\\}.*\n\\*\\*\\* .+ \\*\\*\\*\\*\\|[0-9]+\\(,[0-9]+\\)?[acd][0-9]+\\(,[0-9]+\\)?\\)$"))
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(defconst diff-file-header-re (concat "^\\(--- .+\n\\+\\+\\+ \\|\\*\\*\\* .+\n--- \\|[^-+!<>0-9@* ]\\).+\n" (substring diff-hunk-header-re 1)))
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(defvar diff-narrowed-to nil)

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(defun diff-hunk-style (&optional style)
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  (when (looking-at diff-hunk-header-re)
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    (setq style (cdr (assq (char-after) '((?@ . unified) (?* . context)))))
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    (goto-char (match-end 0)))
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  style)

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(defun diff-end-of-hunk (&optional style donttrustheader)
  (let (end)
    (when (looking-at diff-hunk-header-re)
      ;; Especially important for unified (because headers are ambiguous).
      (setq style (diff-hunk-style style))
      (goto-char (match-end 0))
      (when (and (not donttrustheader) (match-end 2))
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        (let* ((nold (string-to-number (match-string 2)))
               (nnew (string-to-number (match-string 4)))
               (endold
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        (save-excursion
          (re-search-forward (if diff-valid-unified-empty-line
                                 "^[- \n]" "^[- ]")
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                                     nil t nold)
                  (line-beginning-position 2)))
               (endnew
                ;; The hunk may end with a bunch of "+" lines, so the `end' is
                ;; then further than computed above.
                (save-excursion
                  (re-search-forward (if diff-valid-unified-empty-line
                                         "^[+ \n]" "^[+ ]")
                                     nil t nnew)
                  (line-beginning-position 2))))
          (setq end (max endold endnew)))))
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    ;; We may have a first evaluation of `end' thanks to the hunk header.
    (unless end
      (setq end (and (re-search-forward
                      (case style
                        (unified (concat (if diff-valid-unified-empty-line
                                             "^[^-+# \\\n]\\|" "^[^-+# \\]\\|")
                                         ;; A `unified' header is ambiguous.
                                         diff-file-header-re))
                        (context "^[^-+#! \\]")
                        (normal "^[^<>#\\]")
                        (t "^[^-+#!<> \\]"))
                      nil t)
                     (match-beginning 0)))
      (when diff-valid-unified-empty-line
        ;; While empty lines may be valid inside hunks, they are also likely
        ;; to be unrelated to the hunk.
        (goto-char (or end (point-max)))
        (while (eq ?\n (char-before (1- (point))))
          (forward-char -1)
          (setq end (point)))))
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    ;; The return value is used by easy-mmode-define-navigation.
    (goto-char (or end (point-max)))))
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(defun diff-beginning-of-hunk (&optional try-harder)
  "Move back to beginning of hunk.
If TRY-HARDER is non-nil, try to cater to the case where we're not in a hunk
but in the file header instead, in which case move forward to the first hunk."
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  (beginning-of-line)
  (unless (looking-at diff-hunk-header-re)
    (forward-line 1)
    (condition-case ()
	(re-search-backward diff-hunk-header-re)
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      (error
       (if (not try-harder)
           (error "Can't find the beginning of the hunk")
         (diff-beginning-of-file-and-junk)
         (diff-hunk-next))))))
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(defun diff-unified-hunk-p ()
  (save-excursion
    (ignore-errors
      (diff-beginning-of-hunk)
      (looking-at "^@@"))))

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(defun diff-beginning-of-file ()
  (beginning-of-line)
  (unless (looking-at diff-file-header-re)
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    (let ((start (point))
          res)
      ;; diff-file-header-re may need to match up to 4 lines, so in case
      ;; we're inside the header, we need to move up to 3 lines forward.
      (forward-line 3)
      (if (and (setq res (re-search-backward diff-file-header-re nil t))
               ;; Maybe the 3 lines forward were too much and we matched
               ;; a file header after our starting point :-(
               (or (<= (point) start)
                   (setq res (re-search-backward diff-file-header-re nil t))))
          res
        (goto-char start)
        (error "Can't find the beginning of the file")))))
        
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(defun diff-end-of-file ()
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  (re-search-forward "^[-+#!<>0-9@* \\]" nil t)
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  (re-search-forward (concat "^[^-+#!<>0-9@* \\]\\|" diff-file-header-re)
		     nil 'move)
  (if (match-beginning 1)
      (goto-char (match-beginning 1))
    (beginning-of-line)))
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;; Define diff-{hunk,file}-{prev,next}
(easy-mmode-define-navigation
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 diff-hunk diff-hunk-header-re "hunk" diff-end-of-hunk diff-restrict-view
 (if diff-auto-refine
     (condition-case-no-debug nil (diff-refine-hunk) (error nil))))

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(easy-mmode-define-navigation
 diff-file diff-file-header-re "file" diff-end-of-hunk)
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(defun diff-restrict-view (&optional arg)
  "Restrict the view to the current hunk.
If the prefix ARG is given, restrict the view to the current file instead."
  (interactive "P")
  (save-excursion
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    (if arg (diff-beginning-of-file) (diff-beginning-of-hunk 'try-harder))
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    (narrow-to-region (point)
		      (progn (if arg (diff-end-of-file) (diff-end-of-hunk))
			     (point)))
    (set (make-local-variable 'diff-narrowed-to) (if arg 'file 'hunk))))


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(defun diff-hunk-kill ()
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  "Kill current hunk."
  (interactive)
  (diff-beginning-of-hunk)
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  (let* ((start (point))
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	 (nexthunk (when (re-search-forward diff-hunk-header-re nil t)
		     (match-beginning 0)))
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	 (firsthunk (ignore-errors
		      (goto-char start)
		      (diff-beginning-of-file) (diff-hunk-next) (point)))
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	 (nextfile (ignore-errors (diff-file-next) (point)))
	 (inhibit-read-only t))
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    (goto-char start)
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    (if (and firsthunk (= firsthunk start)
	     (or (null nexthunk)
		 (and nextfile (> nexthunk nextfile))))
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	;; It's the only hunk for this file, so kill the file.
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	(diff-file-kill)
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      (diff-end-of-hunk)
      (kill-region start (point)))))

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;; "index ", "old mode", "new mode", "new file mode" and
;; "deleted file mode" are output by git-diff.
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(defconst diff-file-junk-re 
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  "diff \\|index \\|\\(?:deleted file\\|new\\(?: file\\)?\\|old\\) mode")
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(defun diff-beginning-of-file-and-junk ()
  "Go to the beginning of file-related diff-info.
This is like `diff-beginning-of-file' except it tries to skip back over leading
data such as \"Index: ...\" and such."
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  (let* ((orig (point))
         ;; Skip forward over what might be "leading junk" so as to get
         ;; closer to the actual diff.
         (_ (progn (beginning-of-line)
                   (while (looking-at diff-file-junk-re)
                     (forward-line 1))))
         (start (point))
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         (prevfile (condition-case err
                       (save-excursion (diff-beginning-of-file) (point))
                     (error err)))
         (err (if (consp prevfile) prevfile))
         (nextfile (ignore-errors
                     (save-excursion
                       (goto-char start) (diff-file-next) (point))))
         ;; prevhunk is one of the limits.
         (prevhunk (save-excursion
                     (ignore-errors
                       (if (numberp prevfile) (goto-char prevfile))
                       (diff-hunk-prev) (point))))
         (previndex (save-excursion
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                      (forward-line 1)  ;In case we're looking at "Index:".
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                      (re-search-backward "^Index: " prevhunk t))))
    ;; If we're in the junk, we should use nextfile instead of prevfile.
    (if (and (numberp nextfile)
             (or (not (numberp prevfile))
                 (and previndex (> previndex prevfile))))
        (setq prevfile nextfile))
    (if (and previndex (numberp prevfile) (< previndex prevfile))
        (setq prevfile previndex))
    (if (and (numberp prevfile) (<= prevfile start))
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          (progn
            (goto-char prevfile)
            ;; Now skip backward over the leading junk we may have before the
            ;; diff itself.
            (while (save-excursion
                     (and (zerop (forward-line -1))
                          (looking-at diff-file-junk-re)))
              (forward-line -1)))
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      ;; File starts *after* the starting point: we really weren't in
      ;; a file diff but elsewhere.
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      (goto-char orig)
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      (signal (car err) (cdr err)))))
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(defun diff-file-kill ()
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  "Kill current file's hunks."
  (interactive)
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  (let ((orig (point))
        (start (progn (diff-beginning-of-file-and-junk) (point)))
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	 (inhibit-read-only t))
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    (diff-end-of-file)
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    (if (looking-at "^\n") (forward-char 1)) ;`tla' generates such diffs.
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    (if (> orig (point)) (error "Not inside a file diff"))
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    (kill-region start (point))))

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(defun diff-kill-junk ()
  "Kill spurious empty diffs."
  (interactive)
  (save-excursion
    (let ((inhibit-read-only t))
      (goto-char (point-min))
      (while (re-search-forward (concat "^\\(Index: .*\n\\)"
					"\\([^-+!* <>].*\n\\)*?"
					"\\(\\(Index:\\) \\|"
					diff-file-header-re "\\)")
				nil t)
	(delete-region (if (match-end 4) (match-beginning 0) (match-end 1))
		       (match-beginning 3))
	(beginning-of-line)))))

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(defun diff-count-matches (re start end)
  (save-excursion
    (let ((n 0))
      (goto-char start)
      (while (re-search-forward re end t) (incf n))
      n)))

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(defun diff-splittable-p ()
  (save-excursion
    (beginning-of-line)
    (and (looking-at "^[-+ ]")
         (progn (forward-line -1) (looking-at "^[-+ ]"))
         (diff-unified-hunk-p))))

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(defun diff-split-hunk ()
  "Split the current (unified diff) hunk at point into two hunks."
  (interactive)
  (beginning-of-line)
  (let ((pos (point))
	(start (progn (diff-beginning-of-hunk) (point))))
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    (unless (looking-at diff-hunk-header-re-unified)
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      (error "diff-split-hunk only works on unified context diffs"))
    (forward-line 1)
    (let* ((start1 (string-to-number (match-string 1)))
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	   (start2 (string-to-number (match-string 3)))
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	   (newstart1 (+ start1 (diff-count-matches "^[- \t]" (point) pos)))
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	   (newstart2 (+ start2 (diff-count-matches "^[+ \t]" (point) pos)))
	   (inhibit-read-only t))
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      (goto-char pos)
      ;; Hopefully the after-change-function will not screw us over.
      (insert "@@ -" (number-to-string newstart1) ",1 +"
	      (number-to-string newstart2) ",1 @@\n")
      ;; Fix the original hunk-header.
      (diff-fixup-modifs start pos))))
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;;;;
;;;; jump to other buffers
;;;;

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(defvar diff-remembered-files-alist nil)
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(defvar diff-remembered-defdir nil)
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(defun diff-filename-drop-dir (file)
  (when (string-match "/" file) (substring file (match-end 0))))

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(defun diff-merge-strings (ancestor from to)
  "Merge the diff between ANCESTOR and FROM into TO.
Returns the merged string if successful or nil otherwise.
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The strings are assumed not to contain any \"\\n\" (i.e. end of line).
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If ANCESTOR = FROM, returns TO.
If ANCESTOR = TO, returns FROM.
The heuristic is simplistic and only really works for cases
like \(diff-merge-strings \"b/foo\" \"b/bar\" \"/a/c/foo\")."
  ;; Ideally, we want:
  ;;   AMB ANB CMD -> CND
  ;; but that's ambiguous if `foo' or `bar' is empty:
  ;; a/foo a/foo1 b/foo.c -> b/foo1.c but not 1b/foo.c or b/foo.c1
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  (let ((str (concat ancestor "\n" from "\n" to)))
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    (when (and (string-match (concat
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			      "\\`\\(.*?\\)\\(.*\\)\\(.*\\)\n"
			      "\\1\\(.*\\)\\3\n"
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			      "\\(.*\\(\\2\\).*\\)\\'") str)
	       (equal to (match-string 5 str)))
      (concat (substring str (match-beginning 5) (match-beginning 6))
	      (match-string 4 str)
	      (substring str (match-end 6) (match-end 5))))))

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(defun diff-tell-file-name (old name)
  "Tell Emacs where the find the source file of the current hunk.
If the OLD prefix arg is passed, tell the file NAME of the old file."
  (interactive
   (let* ((old current-prefix-arg)
	  (fs (diff-hunk-file-names current-prefix-arg)))
     (unless fs (error "No file name to look for"))
     (list old (read-file-name (format "File for %s: " (car fs))
			       nil (diff-find-file-name old) t))))
  (let ((fs (diff-hunk-file-names old)))
    (unless fs (error "No file name to look for"))
    (push (cons fs name) diff-remembered-files-alist)))
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(defun diff-hunk-file-names (&optional old)
  "Give the list of file names textually mentioned for the current hunk."
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  (save-excursion
    (unless (looking-at diff-file-header-re)
      (or (ignore-errors (diff-beginning-of-file))
	  (re-search-forward diff-file-header-re nil t)))
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    (let ((limit (save-excursion
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		   (condition-case ()
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		       (progn (diff-hunk-prev) (point))
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		     (error (point-min)))))
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	  (header-files
	   (if (looking-at "[-*][-*][-*] \\(\\S-+\\)\\(\\s-.*\\)?\n[-+][-+][-+] \\(\\S-+\\)")
	       (list (if old (match-string 1) (match-string 3))
		     (if old (match-string 3) (match-string 1)))
	     (forward-line 1) nil)))
      (delq nil
	    (append
	     (when (and (not old)
			(save-excursion
			  (re-search-backward "^Index: \\(.+\\)" limit t)))
	       (list (match-string 1)))
	     header-files
	     (when (re-search-backward
		    "^diff \\(-\\S-+ +\\)*\\(\\S-+\\)\\( +\\(\\S-+\\)\\)?"
		    nil t)
	       (list (if old (match-string 2) (match-string 4))
		     (if old (match-string 4) (match-string 2)))))))))

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(defun diff-find-file-name (&optional old batch prefix)
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  "Return the file corresponding to the current patch.
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Non-nil OLD means that we want the old file.
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Non-nil BATCH means to prefer returning an incorrect answer than to prompt
the user.
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PREFIX is only used internally: don't use it."
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  (unless (equal diff-remembered-defdir default-directory)
    ;; Flush diff-remembered-files-alist if the default-directory is changed.
    (set (make-local-variable 'diff-remembered-defdir) default-directory)
    (set (make-local-variable 'diff-remembered-files-alist) nil))
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  (save-excursion
    (unless (looking-at diff-file-header-re)
      (or (ignore-errors (diff-beginning-of-file))
	  (re-search-forward diff-file-header-re nil t)))
    (let ((fs (diff-hunk-file-names old)))
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      (if prefix (setq fs (mapcar (lambda (f) (concat prefix f)) fs)))
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      (or
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       ;; use any previously used preference
       (cdr (assoc fs diff-remembered-files-alist))
       ;; try to be clever and use previous choices as an inspiration
       (dolist (rf diff-remembered-files-alist)
	 (let ((newfile (diff-merge-strings (caar rf) (car fs) (cdr rf))))
	   (if (and newfile (file-exists-p newfile)) (return newfile))))
       ;; look for each file in turn.  If none found, try again but
       ;; ignoring the first level of directory, ...
       (do* ((files fs (delq nil (mapcar 'diff-filename-drop-dir files)))
	     (file nil nil))
	   ((or (null files)
		(setq file (do* ((files files (cdr files))
				 (file (car files) (car files)))
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			       ;; Use file-regular-p to avoid
			       ;; /dev/null, directories, etc.
			       ((or (null file) (file-regular-p file))
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				file))))
	    file))
       ;; <foo>.rej patches implicitly apply to <foo>
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       (and (string-match "\\.rej\\'" (or buffer-file-name ""))
	    (let ((file (substring buffer-file-name 0 (match-beginning 0))))
	      (when (file-exists-p file) file)))
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       ;; If we haven't found the file, maybe it's because we haven't paid
       ;; attention to the PCL-CVS hint.
       (and (not prefix)
	    (boundp 'cvs-pcl-cvs-dirchange-re)
	    (save-excursion
	      (re-search-backward cvs-pcl-cvs-dirchange-re nil t))
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	    (diff-find-file-name old batch (match-string 1)))
       ;; Invent something, if necessary.
       (when batch
         (or (car fs) default-directory))
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       ;; if all else fails, ask the user
       (let ((file (read-file-name (format "Use file %s: " (or (first fs) ""))
				   nil (first fs) t (first fs))))
	 (set (make-local-variable 'diff-remembered-files-alist)
	      (cons (cons fs file) diff-remembered-files-alist))
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	 file)))))

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(defun diff-ediff-patch ()
  "Call `ediff-patch-file' on the current buffer."
  (interactive)
  (condition-case err
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      (ediff-patch-file nil (current-buffer))
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    (wrong-number-of-arguments (ediff-patch-file))))

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;;;;
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;;;; Conversion functions
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;;;;
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;;(defvar diff-inhibit-after-change nil
;;  "Non-nil means inhibit `diff-mode's after-change functions.")

(defun diff-unified->context (start end)
  "Convert unified diffs to context diffs.
START and END are either taken from the region (if a prefix arg is given) or
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else cover the whole buffer."
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  (interactive (if (or current-prefix-arg (and transient-mark-mode mark-active))
		   (list (region-beginning) (region-end))
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		 (list (point-min) (point-max))))
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  (unless (markerp end) (setq end (copy-marker end t)))
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  (let (;;(diff-inhibit-after-change t)
	(inhibit-read-only t))
    (save-excursion
      (goto-char start)
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      (while (and (re-search-forward
                   (concat "^\\(\\(---\\) .+\n\\(\\+\\+\\+\\) .+\\|"
                           diff-hunk-header-re-unified ".*\\)$")
                   nil t)
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		  (< (point) end))
	(combine-after-change-calls
	  (if (match-beginning 2)
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	      ;; we matched a file header
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	      (progn
		;; use reverse order to make sure the indices are kept valid
		(replace-match "---" t t nil 3)
		(replace-match "***" t t nil 2))
	    ;; we matched a hunk header
	    (let ((line1 (match-string 4))
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		  (lines1 (if (match-end 5)
                              (string-to-number (match-string 5)) 1))
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		  (line2 (match-string 6))
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		  (lines2 (if (match-end 7)
                              (string-to-number (match-string 7)) 1))
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		  ;; Variables to use the special undo function.
		  (old-undo buffer-undo-list)
		  (old-end (marker-position end))
		  (start (match-beginning 0))
		  (reversible t))
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	      (replace-match
	       (concat "***************\n*** " line1 ","
		       (number-to-string (+ (string-to-number line1)
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					    lines1 -1)) " ****"))
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	      (save-restriction
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		(narrow-to-region (line-beginning-position 2)
                                  ;; Call diff-end-of-hunk from just before
                                  ;; the hunk header so it can use the hunk
                                  ;; header info.
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				  (progn (diff-end-of-hunk 'unified) (point)))
		(let ((hunk (buffer-string)))
		  (goto-char (point-min))
		  (if (not (save-excursion (re-search-forward "^-" nil t)))
		      (delete-region (point) (point-max))
		    (goto-char (point-max))
		    (let ((modif nil) last-pt)
		      (while (progn (setq last-pt (point))
				    (= (forward-line -1) 0))
			(case (char-after)
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			  (?\s (insert " ") (setq modif nil) (backward-char 1))
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			  (?+ (delete-region (point) last-pt) (setq modif t))
			  (?- (if (not modif)
				  (progn (forward-char 1)
					 (insert " "))
				(delete-char 1)
				(insert "! "))
			      (backward-char 2))
			  (?\\ (when (save-excursion (forward-line -1)
						     (= (char-after) ?+))
				 (delete-region (point) last-pt) (setq modif t)))
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                          ;; diff-valid-unified-empty-line.
                          (?\n (insert "  ") (setq modif nil) (backward-char 2))
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			  (t (setq modif nil))))))
		  (goto-char (point-max))
		  (save-excursion
		    (insert "--- " line2 ","
			    (number-to-string (+ (string-to-number line2)
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						 lines2 -1))
                            " ----\n" hunk))
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		  ;;(goto-char (point-min))
		  (forward-line 1)
		  (if (not (save-excursion (re-search-forward "^+" nil t)))
		      (delete-region (point) (point-max))
		    (let ((modif nil) (delete nil))
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		      (if (save-excursion (re-search-forward "^\\+.*\n-" nil t))
                          ;; Normally, lines in a substitution come with
                          ;; first the removals and then the additions, and
                          ;; the context->unified function follows this
                          ;; convention, of course.  Yet, other alternatives
                          ;; are valid as well, but they preclude the use of
                          ;; context->unified as an undo command.
			  (setq reversible nil))
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		      (while (not (eobp))
			(case (char-after)
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			  (?\s (insert " ") (setq modif nil) (backward-char 1))
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			  (?- (setq delete t) (setq modif t))
			  (?+ (if (not modif)
				  (progn (forward-char 1)
					 (insert " "))
				(delete-char 1)
				(insert "! "))
			      (backward-char 2))
			  (?\\ (when (save-excursion (forward-line 1)
						     (not (eobp)))
				 (setq delete t) (setq modif t)))
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                          ;; diff-valid-unified-empty-line.
                          (?\n (insert "  ") (setq modif nil) (backward-char 2)
                               (setq reversible nil))
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			  (t (setq modif nil)))
			(let ((last-pt (point)))
			  (forward-line 1)
			  (when delete
			    (delete-region last-pt (point))
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			    (setq delete nil)))))))
		(unless (or (not reversible) (eq buffer-undo-list t))
                  ;; Drop the many undo entries and replace them with
                  ;; a single entry that uses diff-context->unified to do
                  ;; the work.
		  (setq buffer-undo-list
			(cons (list 'apply (- old-end end) start (point-max)
				    'diff-context->unified start (point-max))
			      old-undo)))))))))))
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(defun diff-context->unified (start end &optional to-context)
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  "Convert context diffs to unified diffs.